Abstract In an ongoing project, we are finding that a contingency management (CM) intervention reinforcing attendance at outpatient substance abuse treatment decreases objective indices of drinking. Benefits of CM are noted during the intervention period and long term, even after the reinforcement for attending treatment ends. These preliminary results reinforcing attendance are excellent, and we hope to replicate and extend the beneficial impact of the CM intervention in the proposed study. In our ongoing study, we are using transdermal alcohol technology to assess drinking. This technology accurately assesses alcohol use in the natural environment, but it is bulky to wear and expensive, limiting its use in clinical settings. In this project, we will evaluate the use of another objective indicator of drinking. Phosphatidylethanol (PEth) is a direct biomarker of alcohol that can detect moderate to heavy drinking with high sensitivity and specificity over 3-week periods. Reinforcing negative PEth results alongside attendance may increase the proportion of patients who respond to CM during and post treatment. In the proposed study, we will collect PEth samples every 3 weeks for 12 weeks in 150 patients initiating outpatient treatment for alcohol use disorders. Using a two-group randomized design, patients will be assigned to standard care with PEth monitoring alone or with CM for attending treatment and submitting PEth negative samples. Compared to standard care and monitoring, we expect that the CM intervention will result in greater attendance, more PEth negative samples, and higher proportions of self-reported non-drinking days, along with lower proportions of heavy drinking days, over the short term and the long term, measured throughout a 12-month follow-up. We anticipate that the reinforcement intervention will decrease other drug use and sexual risk behaviors that spread HIV, reduce psychiatric symptoms, and improve quality of life as well. We will also evaluate the cost- effectiveness of this intervention. Although it adds costs, CM may be cost-effective in improving outcomes and reducing personal and societal harms associated with alcohol use disorders, and reinforcing attendance may enhance clinic reimbursement rates. Results from this study will be important for paving the way toward integrating CM in the treatment of alcohol use disorders and for using this biomarker of alcohol use in clinical trials and practice settings more generally. PEth, with a 3-week time frame, may be an ideal method to monitor outcomes in many populations of drinkers and to reinforce the absence of hazardous drinking once patients engage in care and achieve initial periods of abstinence or greatly reduced drinking.